In recent years, in fields of rotary machines, medium or small sized transformers, electrical components and the like, which use non-oriented electrical steel sheets as materials of their iron cores, a demand for realization of high-efficiency and miniaturization is increasing more and more, in the movement of global environmental conservation typified by the worldwide power and energy saving and CO2 reduction and the like. Under such a social environment, an improvement in performance of the non-oriented electrical steel sheet is of course a pressing issue.
Further, according to the usage, favorable magnetic properties in a rolling direction are sometimes required for a non-oriented electrical steel sheet. For example, a non-oriented electrical steel sheet used for a divided iron core among iron cores of rotary machines, and a non-oriented electrical steel sheet used for iron cores of medium or small sized transformers, are sometimes required to improve magnetic properties in a rolling direction. In these iron cores, magnetic fluxes mainly flow in orthogonal two directions. Further, it is often the case that the rolling direction of the non-oriented electrical steel sheet is set to one direction, out of these two directions, in which an influence of the flow of the magnetic flux is particularly large.
Accordingly, various techniques have been conventionally proposed for the purpose of improving the magnetic properties of the non-oriented electrical steel sheet.
For example, a technique of increasing contents of Si and Al for the purpose of reducing an iron loss has been proposed. For instance, Patent Literature 1 describes a non-oriented electrical steel sheet in which an Al content is increased while keeping a relatively low Si content for the purpose of improving workability during performing cold-rolling. A technique in which not only the increase in contents of Si and/or Al and the like but also the reduction in contents of C, S, N and the like is realized, has also been proposed. Techniques of reducing an iron loss by making impurities harmless through chemical treatment such as an addition of Ca (Patent Literature 2), and an addition of REM (Patent Literature 3), have also been proposed. Further, Patent Literature 4 describes a technique regarding a condition of finish annealing.
For example, a technique regarding an improvement in magnetic flux density has also been proposed. For instance, Patent Literature 5 describes a technique regarding a condition of hot-rolled sheet annealing and a condition of cold-rolling. Further, Patent Literature 6 describes a technique regarding an addition of alloying elements of Sn, Cu and the like.
However, with the conventional techniques, it is difficult to sufficiently improve the magnetic properties in the rolling direction of the non-oriented electrical steel sheet. Further, with the technique in which the contents of Si and Al are increased for the purpose of reducing the iron loss, a saturation magnetic flux density becomes low. In particular, Al easily reduces the saturation magnetic flux density, when compared to Si, so that with the technique described in Patent Literature 1, the saturation magnetic flux density becomes extremely low. Such a technique in which the saturation magnetic flux density becomes low, is absolutely inappropriate for the miniaturization of electric equipments.